A motor controller for use in motor control is heavily used in industrial machines such as an electronic packaging machine, semiconductor manufacturing equipment, a machine tool, and a machine used in the field of factory automation and robotics. The motor controller can include a feedforward controller that calculates an operation command signal on the basis of an arbitrary positioning command and a mathematical model of a controlled object, and a feedback controller that reduces an error signal obtained by subtracting an angle of rotation or a position signal of the motor from the operation command signal. Such a motor controller enables a movable part including a working machine such as a robot hand attached to the motor to perform positioning at high speed and with high precision.
The motor is set up on a stand or machine stand of the industrial machine where, when the stand or machine stand has low stiffness, vibration of the stand accompanying reaction force of the motor causes a decrease in the positioning performance of the movable part attached to the motor. The motor controller can thus be equipped with a vibration suppression compensator, which is also referred to as a command filter or pre-filter (Patent Literature 1). The vibration suppression compensator operates the operation command signal on the basis of a natural frequency and an attenuation coefficient of the stand or machine stand in order to drive the motor while suppressing vibration of the stand or machine stand.
The natural frequency of the stand or machine stand varies depending on the installation environment of the entire industrial machine or the attitude of a controlled object. Accordingly, a true value of a control parameter set in the vibration suppression compensator varies depending on a positioning site so that the effect of vibration suppression cannot be fully achieved. Now, in order to compensate for the reduction in robustness against the change in the true value of the parameter, Patent Literature 1 proposes machine stand acceleration feedback. The machine stand acceleration feedback is performed such that a signal detected by an acceleration sensor installed on the stand or machine stand is subjected to filtering with a band pass characteristic that allows a signal in an arbitrary frequency band to pass as well as an adjustment using a proportional gain, and then the signal is fed back as driving force of the motor.
Patent Literature 2 proposes surface plate acceleration feedback for an X-Y stage positioning apparatus including a liner motor mounted on a vibration isolator that is treated as a surface plate. While considering the mass of a movable part driven by an X-Y stage and the gain of a power amplifier, the surface plate acceleration feedback is performed such that a signal from an acceleration sensor installed on the vibration isolator is subjected to filtering with a low-pass characteristic or band pass characteristic as well as an adjustment using a proportional gain, and then the signal is fed back as driving force of the motor.